/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jena.graph.compose;

import org.apache.jena.graph.*;
import org.apache.jena.util.iterator.*;

/**
 * Class representing the dynamic set difference L - R of two graphs. This is
 * updatable; the updates are written through to one or other of the base graphs.
 */
public class Difference extends Dyadic implements Graph {
    /**
     * Initialise a graph representing the difference L - R.
     */
    public Difference(Graph L, Graph R) {
        super(L, R);
    }

    /**
     * Add a triple to the difference: add it to the left operand, and remove it from
     * the right operand.
     */
    @Override
    public void performAdd(Triple t) {
        L.add(t);
        R.delete(t);
    }

    /**
     * Remove a triple from the difference: remove it from the left operand. [It
     * could be added to the right operand instead, but somehow that feels less
     * satisfactory.]
     */
    @Override
    public void performDelete(Triple t) {
        L.delete(t);
    }

    @Override
    public ExtendedIterator<Triple> _graphBaseFind(Triple t) {
        return L.find(t).filterDrop(ifIn(R));
    }
}
